Polycystic Kidney Disease (PKD) causes renal failure due to progressive tubular cystic expansion. Mutations of PKD1 are responsible for 85% of ADPKD (autosomal dominant PKD), and the gene product (polycystin-1, PC1) is a large complex protein. Polycystin-1 interacts with numerous proteins and is found in cilia, the junctional complex and at the basal surface. Abnormalities in PKD include alterations in cell-cell adhesion and cell-matrix interactions contributing to loss of normal tubule structure. The C terminus of PC1 interacts with G proteins, and we have identified binding of Ga12, but not Ga13 to the PC1 C terminus. Ga12 is also found in the epithelial cell junctional complex where it regulates permeability and cell-cell interactions. Preliminary studies reveal that cell attachment and migration on collagen-1 are regulated by Ga12 and a2b1 integrins, and activating Ga12 leads to cyst formation in tubulogenesis assays. In MDCK cells over expressing full length PC1, increased tubulogenesis is blocked by thrombin activation of endogenous Ga12 and leads to cyst formation. In a novel assay of activated Ga12, increasing or decreasing PC1 levels in MDCK cells significantly affects Ga12 activation. We hypothesize that PC1 regulates Ga12 and integrins to modulate cell matrix interactions, cell-cell adhesion and cell migration essential for normal tubule development. These studies will colocalize Ga12, integrins and PC1 in cultured renal epithelial cells and mouse kidney, and will identify the macromolecular complex through immunoprecipitation studies and mass spectrometry (Aim 1). Ga12 regulation of cell-cell adhesion, cell-matrix interaction and cell migration via integrins will be explored in Aim 2, and the role of PC1 in these signaling pathways will be elucidated in cell culture models. In Aim 3, the effect of PC1 on regulating Ga12/integrin signaling in tubulogenesis assays will be used to identify the role of these pathways in tubule development. The mechanisms leading to cyst development in vivo will be explored using a2 integrin knockout mice, PC1 null heterozyotes and gGT-Cre/QLa12 mice. PUBLIC HEALTH RELEVANCE: Polycystic Kidney Disease (PKD) causes renal failure due to progressive tubular cystic expansion. Normal kidney development is complex and requires coordinated events (signals) that regulate cell interactions with neighboring cells and the underlying support. In PKD, these signals are altered and lead to cyst formation. These studies will reveal new treatment strategies to correct these abnormal signals in PKD.